There exists a magnetic resonance wireless power transmission system that performs wireless power transmission by magnetic resonance. The magnetic resonance wireless power transmission system has a power transmitter including a resonance coil and a power receiver including a resonance coil, and the resonance coil included in the power transmitter and the resonance coil included in the power receiver have the same resonance frequency.
When power is supplied to the resonance coil of the power transmitter and an alternating current having the same frequency as the resonance frequency of the resonance coil is caused to flow, power is transmitted by magnetic resonance between the resonance coil of the power transmitter and the resonance coil of the power receiver and an alternating current flows through the resonance coil of the power receiver. In this manner, power is transmitted from the power transmitter to the power receiver wirelessly.
As the wireless power transmission system, there exist, for example, a wireless power transmission system using electric waves and a wireless power transmission system using electromagnetic induction in addition to the magnetic resonance wireless power transmission system. Compared to those other power transmission systems, the magnetic resonance wireless power transmission system has, for example, the following merits. It is possible for the magnetic resonance wireless power transmission system to transmit large power compared to the wireless power transmission system using electric waves. Further, it is possible for the magnetic resonance wireless power transmission system to extend the power transmission distance compared to the wireless power transmission system using electromagnetic induction and also possible to downsize each resonance coil of the power transmitter and the power receiver.
On the other hand, in the wireless power transmission system, it is necessary to perform wireless communication between the power transmitter and the power receiver in order to grasp the transmitted power to determine an electric power rate in accordance with the transmitted power and to prevent power transmission to other than the transmission target by authenticating the power receiver.
Hence, it is considered to provide a function to perform wireless communication also in the magnetic resonance wireless power transmission system.
For example, there is a technique to transmit the charge level of a built-in power source of an implantable micro stimulator to outside by non-contact communication (e.g. Japanese National Publication of International Patent Application No. 2005-531371). Further, there is a technique that uses a magnetic field and resonance for non-contact communication (e.g. Japanese National Publication of International Patent Application No. 2008-535611, Japanese Laid-Open Patent Publication No. 06-54824, and Japanese Examined Patent Application Publication No. 08-29143).
However, if the already existing non-contact communication function is simply added to the magnetic resonance wireless power transmission system, there is a possibility that the costs of the power transmitter and the power receiver increase because it is necessary to newly provide a communication module to the power transmitter and the power receiver.